Process for the commercial production of polyhydroxy alcohols and glycols

Abstract

An aldolisation process is disclosed for converting an aldehyde or mixture of aldehydes, such as iso-butyraldehyde and formaldehyde, to a desired polyhydroxy alcohol or glycol, such as neopentyl glycol. Aldolisation is effected in a stirred tank reactor using an alkali catalyst, such as sodium hydroxide. An aldolisation intermediate product is converted to the desired polyhydroxy alcohol or glycol by a hydrogenation or cross-Cannizzaro reaction step. The product is recovered and an aqueous catalyst-containing phase is recycled to the aldolisation zone. At least a portion of this catalyst recycle stream is purged to control the build up of cross-Cannizzaro products in the recycle stream. The purge stream is treated electrolytically to obtain an aqueous catalyst-containing solution for recycle to the aldolisation zone and an effluent stream comprising volatile organic materials and being substantially free from alkali catalyst.

Claims

1. A process for the production of a compound having the formula: ##STR15## in which R.sup.1 and R.sup.4 each represent, independently of the other, a hydrogen atom, an alkyl group, an aralkyl group, or an aryl group; and

R.sup.2 and R.sup.3 each represent, independently of the other, an alkyl group, a hydroxyalkyl group, an aralkyl group, an arylhydroxyalkyl group, or an aryl group; which process comprises:

(a) reacting one mole of a first aldehyde having at least one.alpha.-hydrogen atom and having the formula: ##STR16## in which R.sup.5 is a hydrogen atom, an alkyl group, an aralkyl group, or an aryl group; and R.sup.6 is a hydrogen atom, an alkyl group, an aralkyl group, or an aryl group; with at least one mole of a second aldehyde having the formula:

in which R.sup.7 is a hydrogen atom, an alkyl group or an aryl group; under aldolisation conditions in the presence of an aldolisation catalyst selected from alkali metal hydroxides, alkali metal carbonates, alkali metal bicarbonates, and mixtures thereof, and from alkaline earth metal hydroxides and mixtures thereof with alkali metal hydroxides, thereby to generate an intermediate aldolisation product;

(b) converting the intermediate aldolisation product of step (a) by one or more further steps including a step selected from hydrogenation and a cross-Cannizzaro reaction to the compound having the formula (I);

(c) recovering the compound having the formula (I);

(d) recovering an aqueous spent catalyst phase containing metal values and at least one Cannizzaro or cross-Cannizzaro reaction product or by-product;

(e) passing material of the spent catalyst phase to an electrolysis zone comprising an anode zone containing an anode, a cathode zone containing a cathode, and at least one ion selective barrier means separating the anode zone from the cathode zone;

(f) passing a direct current or rectified alternating current between the anode and the cathode thereby to liberate metal hydroxide in the cathode region, said metal hydroxide being selected from alkali metal hydroxides, alkaline earth metal hydroxides, and mixtures thereof;

(g) recovering liberated metal hydroxide of step (f);

(h) if necessary, converting at least a portion of the liberated metal hydroxide of step (g) to the catalyst of step (a); and

(i) recycling at least one of liberated metal hydroxide of step (g) and converted metal hydroxide of step (h) for use as aldolisation catalyst in step (a).

2. A process according to claim 1, wherein step (g) comprises the steps of:

(j) recovering from the anode region of said electrolysis zone a liquid phase and gas phase;

(k) separating said liquid phase and said gas phase;

(l) steam stripping at least a portion of said liquid phase;

(m) recovering from said stream stripping step (1) an overhead fraction;

(n) condensing said overhead fraction to provide a condensed liquid phase comprising water and steam volatile organic compounds in a form substantially free of said aldolisation catalyst; and

(o) recovering condensed liquid phase from said overhead fraction for recycle to the anode region of said electrolysis zone.

3. A process according to claim 1, wherein the at least one ion selective barrier means is permeable to cations from said aldolisation catalyst and wherein the spent catalyst stream from step (d) is supplied to the anode region of said electrolysis zone.

4. A process according to claim 3, wherein an aqueous phase comprising water is supplied to the cathode region of said electrolysis zone.

5. A process according to claim 1, wherein said at least one ion selective barrier means is permeable to anions and the spent catalyst stream of step (d) is supplied to the cathode region of said electrolysis zone.

6. A process according to claim 5, wherein an aqueous phase comprising water is supplied to the anode region of said electrolysis zone.

7. A process according to claim 1, wherein at least two ion selective barrier means are provided in said electrolysis zone, including a first barrier means permeable to cations and a second barrier means arranged such that said electrolysis zone comprises at least three regions, including a cathode region separated from an intermediate region by said first barrier means and an anode region separated from said intermediate region by said second barrier means, the spent catalyst stream of step (d) being supplied to said intermediate region in between said at least two barrier means.

8. A process according to claim 7, wherein an aqueous phase comprising water is supplied to one or both of the anode region and the cathode region of said electrolysis zone.

9. A process according to claim 1, wherein the anode and cathode of said one or more electrolysis cells are smooth platinum electrodes.

10. A process according to claim 1, wherein said at least one barrier means comprises a membrane permeable to ions.

11. A process according to claim 1, wherein said membrane is a supported ion exchange material.

12. A process according to claim 1, wherein the electrolysis zone is maintained at a temperature of between about 0.degree. C. and about 100.degree. C.

13. A process according to claim 1, wherein R.sup.1, R.sup.4 and R.sup.7 are hydrogen atoms and R.sup.2, R.sup.3, R.sup.5 and R.sup.6 are methyl groups whereby the compound of formula (I) is neopentyl glycol, whereby the first aldehyde of formula (II) is iso-butyvaldehyde, and whereby the second aldehyde of formula (III) is formaldehyde.

14. A process according to claim 13, wherein the intermediate aldolisation product is of formula: ##STR17## and is converted to neopentyl glycol in step (b) by a cross-Cannizzaro reaction.

15. A process according to claim 13, wherein the intermediate aldolisation product is of formula: ##STR18## and is converted to neopentyl glycol in step (b) by hydrogenation.

16. A process according to claim 1, wherein R.sup.1, R.sup.4, R.sup.5, R.sup.6 and R.sup.7 are hydrogen atoms, R.sup.2 is hydroxymethyl group, and R.sup.3 and R.sup.5 are both ethyl groups, whereby the compound of formula (I) is 1,1,1-trimethylolpropane, whereby the first aldehyde of formula (II) is n-butyraldehyde, whereby the second aldehyde of formula (III) is formaldehyde, and wherein the conversion step (b) is a cross-Cannizzaro reaction step.

17. A process according to claim 1, wherein R.sup.1, R.sup.4, R.sup.5, R.sup.6 and R.sup.7 are hydrogen atoms and R.sup.2 and R.sup.3 are both hydroxymethyl groups, whereby the compound of formula (I) is pentaerythritol, whereby the first aldehyde of formula (II) is acetaldehyde, and whereby the second aldehyde of formula (II) is formaldehyde.

18. A process according to claim 17, wherein the conversion step (b) is a cross-Cannizzaro reaction step.

19. A process according to claim 17, wherein the conversion step (b) is a hydrogenation step.

20. A process according to claim 1, wherein R.sup.1 is iso-propyl, R.sup.2, R.sup.3, R.sup.5 and R.sup.6 are methyl groups, R.sup.4 is a hydrogen atom and R.sup.7 is iso-proeyl, whereby the compound of formula (I) is 2,4,4-trimethylpentane-1,3-diol, and whereby the first and second aldehydes of formula (II) and (III) are each iso-butyraldehyde, wherein the intermediate aldolisation product has the formula: ##STR19## and wherein the conversion step (b) is a hydrogenation step.

21. A process for the production of polyhydroxy alcohols and glycols which comprises the steps of:

(A) subjecting at least one aldehyde to aldolisation conditions in the presence of an effective amount of an aldolisation catalyst selected from alkali metal hydroxides, alkali metal carbonates, alkali metal bicarbonates and mixtures thereof, and from alkaline earth metal hydroxides and mixtures thereof with alkali metal hydroxides to form a desired aldol intermediate;

(B) converting said aldol intermediate by means of at least one further reaction step including a reaction step selected from a hydrogenation reaction and a cross-Cannizzaro reaction to form at least one polyhydroxy alcohol or glycol;

(C) recovering from the aldol intermediate conversion step (B) a reaction mixture comprising unreacted aldehyde or aldehydes, water, aldolisation catalyst, at least one polyhydroxy alcohol or glycol, and at least one Cannizzaro or cross-Cannizzaro reaction product;

(D) separating from the reaction mixture a first aqueous phase comprising water, aldolisation catalyst and at least one Cannizzaro or cross-Cannizzaro reaction product;

(E) supplying at least a portion of said first aqueous phase to an electrolysis zone;

(F) electrolysing said portion of said first aqueous phase in said electrolysis zone to generate electrolysis products, including a metal hydroxide selected from said alkali metal hydroxide and said alkaline earth metal hydroxide;

(G) recovering from a cathode region of said electrolysis zone a second aqueous phase, the concentration of said at least one Cannizzaro or cross-Cannizzaro product in said second aqueous phase being below that in said first aqueous phase, said second aqueous phase comprising water and said metal hydroxide;

(H) if necessary converting said metal hydroxide of step (G) to the catalyst of step (A); and

(I) supplying to the aldolisation step as catalyst for step (A) a material selected from the metal hydroxide of step (G) and the converted metal hydroxide of step (H).

22. A process according to claim 1, wherein aldolisation is effected in a stirred tank reactor provided with internal baffles.

23. A process according to claim 1, wherein aldolisation is carried out in an aldolisation zone with a residence time of from about 2 minutes to about 75 minutes.

24. A process according to claim 1, wherein aldolisation is carried out with an organic phase:aqueous phase ratio of from about 15:1 to about 1:15 by volume.

25. A process according to claim 1, wherein aldolisation is carried out in a tank reactor provided with a stirrer and in which the power supplied to the stirrer ranges from about 0.1 to about 3.0 kW/m.sup.3 of liquor.